Ultrasonic diagnostic devices have been used increasingly in recent years, particularly for fetal monitoring and for measuring blood flow (plethysmography). Substances currently used as a couplant material to facilitate transfer of ultrasonic energy to the patient have not been entirely satisfactory. A liquid gel has, for example, been used in the past for ultrasonic procedures. This gel is an amorphous fluid which can be squeezed from a collapsible tube and then applied to the patient by smearing it onto the skin. These fluids are messy and perceived as being cold by the patient. They also require cleanup following use. In addition, if left on the skin for a period of time, they can dry out. Moreover, the thickness of the fluid film applied to the skin is non-uniform. It is believed that this contributes to inconsistencies in the signals received by the ultrasound transducer. For example, when a Doppler wand is used in ultrasound diagnostics, it appears to be differences in the fluid film from one area to another that cause occasional sudden bursts of noise in the signal received. When the operator is using earphones to listen to the Doppler signal being received, artifacts in the signal being received sound like sudden blasts of loud static which is, of course, very objectionable.
One example of a liquid gel is in U.S. Pat. No. 4,002,221 which describes a transducer coupling agent in the form of a gel having a viscosity similar to mayonnaise and formed from copolymers of methylvinyl ether and maleic acid and carboxy polymethylene polymer with alkali metal salts as thickeners. U.S. Pat. No. 4,459,854 describes an ultrasonic transducer coupling member composed of a hydrogel which fits into an opening between interconnected walls that define a generally trapezoidal space for the hyrodgel. The hydrogel is placed in the trapezoidal space. The hydrogel can be a copolymer of vinyl pyrrolidone and phenolethyl methacrylate. Silicone fluid has also been used, but silicones are dielectrics and electrical insulators. In addition, the density of silicone is not the same as that of the body. These factors can interfere with the transfer of electrical and/or sonic energy to and from the body.
It is a general object of the present invention to provide an improved ultrasonic couplant gel which is easily applied to the body and removed, which is flexible and self-supporting, and which conforms readily to the contours of the body and preferably has at least a moderately tacky lower surface to form a mechanical bond with the skin but which can be easily removed later, which is uniform in thickness, facilitates movement of the ultrasound instrument in all directions thereacross, does not tend to contribute to signal noise and will efficiently transmit ultrasonic energy to and from the body. In addition, it is an object to provide a couplant gel which is easy to handle, can be quickly applied to the body by medical personnel and confined to an area of the body having a predetermined perimeter. It is a more specific object to provide a solid couplant gel in sheet form which is suited for various ultrasound application such as fetal monitoring during pregnancy as well a peripheral vascular non-invasive ultrasound measurements which may utilize pulsed Doppler instrumentation to detect blood flow at a specific distance from the ultrasonic probe and for other biomedical applications.
These and other more detailed and specific objects of the present invention will be better understood by reference to the following brief summary which describes by way of example but a few of the various forms of the invention within the scope of the appended claims.